A liquid crystal device (LCD) is a type of display device that is widely used in notebook computers and monitors. The LCD includes a panel for implementing an image, and the panel includes a plurality of pixels. The plurality of pixels are formed at an intersecting area between a plurality of scan lines for transmitting gate selection signals and a plurality of data lines for transmitting color data (i.e., gradation data). A conventional driving circuit for driving a display device such as the LCD will be described with reference to FIG. 1. FIG. 1 is a block diagram of a portion of a conventional driving circuit for driving a display device. Referring to FIG. 1, the driving circuit 10 includes a control register 11 and a logic circuit 12 in addition to a driver (not shown) for driving a panel and a memory (not shown). The control register 11 stores control data HOST_DATA provided from a host. The logic circuit 12 receives the control data HOST_DATA from the control register 11 and performs a logic operation using the control data HOST_DATA. The display device operates in a predetermined way according to a signal corresponding to the operation result, which is generated by the logic circuit 12.
The logic circuit 12 also receives a plurality of control signals in addition to bit values of the control data HOST_DATA output from the control register 11 so as to perform a predetermined logic operation and generates various signals for driving the display device. Although data for setting the control data HOST_DATA stored in the control register 11 is provided from the host in FIG. 1, another portion of the control register 11 may also store control data provided from a storage device such as erasable programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), or dynamic random access memory (DRAM). Since the conventional driving circuit illustrated in FIG. 1 is associated with image implementation, it may cause an abnormal image in a display panel if it malfunctions. For example, an error may occur during driving of the display device due to external causes such as electrostatic discharge (ESD).
FIG. 2 illustrates a case where data stored in the control register 11 is changed by ESD attack. The control register 11 may include a plurality of flip-flops one of which is indicated as 11_1 in FIG. 2. The flip-flop 11_1 stores the control data HOST_DATA provided from the host and outputs the stored control data HOST_DATA to the logic circuit 12 in response to a predetermined clock signal CLK. However, the driving circuit for driving the display device such as the LCD is likely to be exposed to external noise such as ESD during a display operation. Bit values of the control data HOST_DATA stored in the flip-flop 11_1 (e.g., a bit value for setting a common voltage and a bit value for gamma correction) may be changed. For this reason, the logic circuit 12 may malfunction, causing abnormal display in an LCD screen.
In particular, when the control data HOST_DATA is provided to the logic circuit 12 in order to set the display quality property of the display device, the control data HOST_DATA conventionally has fixed data using a metal layer so is not to be changed by an external cause such as ESD attack. A structure for providing fixed control data is as illustrated in FIG. 3. In particular, FIG. 3 is a block diagram of a logic circuit that provides fixed control data according to the prior art. Referring to FIG. 3, the logic circuit includes a flip-flop 21 into which control data HOST_DATA provided from a host and a predetermined clock signal CLK are input and a multiplexer 22 into which fixed control data FIX_DATA provided using a metal layer and an output of the flip-flop 21 are input and which outputs one of the fixed control data FIX_DATA and the output of the flip-flop 21. Thus, control data Ctr_DATA is generated by the logic circuit and a display device driving circuit may include a plurality of logic circuits illustrated in FIG. 3 in order to provide a plurality of control data to the logic circuit 12.
To test the display quality property of the display device, control data in various forms are provided to a plurality of flip-flops from the host. Once bit values of control data capable of optimizing the display quality property according to a test result, the fixed control data FIX_DATA having bit values corresponding to the set bit values is provided to the multiplexer 22. The fixed control data FIX_DATA may be provided using a metal layer connected to a power supply voltage VDD or a ground voltage VSS. For example, a metal line connected to the power supply voltage VDD may be connected to the multiplexer 22 in order to provide the fixed control data FIX_DATA having a bit value of ‘1’, and a metal line connected to the ground voltage VSS may be connected to the multiplexer 22 in order to provide the fixed control data FIX_DATA having a bit value of ‘0’. When the display device is driven, the multiplexer 22 provides the fixed control data FIX_DATA to the logic circuit 12 as the control data Ctr_DATA for setting the display quality property of the display device.
FIG. 4 illustrates a metal layout of a display device driving circuit having the logic circuit illustrated in FIG. 3. To provide the fixed control data Fix_DATA having the bit values corresponding to the test result, a metal layout is implemented in the form as illustrated in FIG. 4. In particular, to provide the fixed control data Fix_DATA of a logic high or low level, a plurality of metal lines selectively connected to a power supply voltage (VDD) line or a ground voltage (VSS) line are required and each of the metal lines provides single fixed control data Fix_DATA.
In general, thousands of bits of control data are required to set the display quality properties of the display device. However, when fixed control data is used to prevent control data from being changed by an external cause, a large amount of control data is required, thereby increasing the number of metal lines for providing the fixed control data. In other words, when the fixed control data is generated using a metal line as illustrated in FIG. 4, a layout for implementing the metal line by become inefficient.